Join Astrophysics after B.Tech Electrical and Electronics? Which exams need to be written and colleges offering the course? Is it necessary to do Ph.D after completion of MSc Astrophysics?

after doing B tech in electrical and electronics how can one join astrophysics? what is the exam to be written? is there any good college in tamil nadu(India)?is it really necessary to do PHd after completion of MSc astrophysics?